1. DSLT Training

2. Contents Introduction to sonic logging Physics of measurement
Hardware Description
Software Description
Operational Hints

3. Why Sonic … ? Formation evaluation Cement bond evaluation
Porosity estimation
Primary porosity
Lithology identification
With other tools
Gas detection
Fractures and permeability
Mechanical properties
Sanding analysis
Wellbore stability
Cement bond evaluation
Geophysical applications
Synthetic seismograms
AVO

4. Why DSLT? The DSLT tool does: The DSLT tool does not:
Provide a sonic tool for FTB telemetry
Provide the first fully digital sonic tool
Provide Dt and CBL applications with existing sondes
The DSLT tool does not:
Replace the DSI for shear and Stoneley applications
Replace the SDT tool for array measurement (DSI is the tool that does so)

5. DSLT Outputs DSLT with SLS-E or SLS-W 2-ft span BHC DT (3-ft to 5-ft)
6-in. span HBHC DT
16-bit VDL
3-ft dual gate CBL with fluid compensation
16-bit waveform recording (BHC and HBHC sequences)

6. DSLT Outputs DSLT with SLS-F or SLS-Z DSLT with SLS-D or SLS-C
2-ft span DDBHC DT (8-ft to 10-ft and 10-ft to 12-ft)
16-bit VDL
16-bit waveform recording (DDBHC sequence)
DSLT with SLS-D or SLS-C
2-ft span DDBHC DT (3-ft to 5-ft and 5-ft to 7-ft)
3-ft dual gate CBL with fluid compensation

7. DSLC Overview MAXIS DSLC New applications: New telemetry applications
Tool Operation Recorder interface
On-Board-Programming interface
DSLC
New telemetry applications
DTS telemetry and tool control
Tool Operation Recorder
New sonic tool features
On-Board-Programming
Digital transit-time detection

8. Wave propagation
A pebble dropped into the water will generate waves that propagate radially away from the source.

9. Wave propagation Pressure Wave
In a similar fashion, the transmitter emits a pressure wave which travels radially in the borehole.

10. Wave propagation Head Waves
An energy source moving through the medium will generate head waves

11. Wave propagation Pressure Wave
When the pressure wave contacts the borehole, it splits into a compressional component (green), a shear component (red) and a mud wave reflection (blue)

12. Wave propagation Head Waves
If the acoustic velocity of the wavefront in the formation is faster than the acoustic velocity of the borehole fluid, the wavefront will become perpendicular to the borehole wall.
The head wave is formed when the wavefront is at right angle to the boundary.

13. Wave propagation References Acoustics Online Training
Sonic Online Training

14. Piezoelectric Receivers
When the pressure wave applies force to the piezoelectric material, it generates a potential which is proportional to the pressure applied.

15. Piezoelectric Transmitters
When voltage is applied to piezoelectric transmitters, they expand creating a pressure wave.

16. Sonic Waveform
When the sonic transmitter is fired, the receiver will see the compressional arrivals first (which are usually in the range of 8-12 kHz), followed by shear arrivals (which are in the order of 1-5 kHz).
The frequency of both arrivals is a function of the formation slowness.
After this, Stoneley arrivals occur (which are guided waves across the borehole).
In slow formations, it is possible not to be able to see the shear arrivals.

17. Dt Measurement: Single Tx-Single Rx
Knowing only the spacing between Tx and Rx, it is not possible to compute formation slowness as mud slowness is not known, and the distances traveled in the formation (b) and the borehole (a and c) are not known.

18. Dt Measurement: Borehole Compensation
TT1 = a + b + c
TT2 = a + d + c
TTformation = TT1 - TT2 = (b - d)
Dtformation = (b - d) / 2

19. Dt Measurement: Sonde Tilt Problem
Sonde tilt will introduce errors in the measurement of Dt as a1 <> a2, and c1 <> c2.
Also (b-d) is no longer equal to the distance between the two receivers of 2 ft, but will be reduced by the cosine of the tilt.

20. Dt Measurement: BHC Sonde Configuration
By adding a symmetrical transmitter and two receivers set, we compensate for both borehole and tilt effects:
Dtformation = ((TT1-TT2)+(TT3-TT4))/4
This is the SLS-E sonde

21. Dt Measurement: DDBHC Sonde Configuration
The results from positions 1 and 2 are added to simulate a BHC measurement:
Dtformation = ((TT1-TT2)+(TT3-TT4))/4
This is the SLS-D/F sonde

22. CBL Measurement CBL is the amplitude at the 3-ft receiver
Zero bond is like ringing a bell
Loud ringing
High amplitude
Good bond is like a blanket on a bell
Much quieter
Low amplitude sound wave

23. VDL Measurement VDL is the wavetrain at the 5-ft receiver
VDL is an indication of both casing-to-cement bond and cement-formation bond.

24. Basic Sonic Measurement
An acoustic pulse is sent into the formation
The time it takes to reach each receiver is measured
One path is 2ft longer than the other.
The extra time that sound takes to travel those 2ft is used to determine rock’s acoustic velocity
2 ft

25. Transit Time
Transit time is: The time it takes sound to travel from the transmitter to the receiver
Measured in s
It contains : TTmud1+TTrock+TTmud2
TT3
TT4

26. Delta-T
The time it takes for sound to travel through a known distance of rock
measured in s/m or s/ft
2ft

27. Delta-T Calculated as the difference between two transit times.
We know the distance between the receivers
2ft

28. Open-Hole waveform shown.
Waveform vs VDL WF
CVDL
VDL
Open-Hole waveform shown.

29. Waveforms & Transit Times
Transmitted Pulse: To
Received Pulses Pulse
Far Receiver TT (TT1 or TT3)
Far Receiver (TT3)
Near Receiver (TT4)
Near Receiver TT (TT2 or TT4)
TT3 - TT4
The extra travel time is caused by the longer travel path.

30. Extra time required to travel 2ft farther
Waveforms & Delta-T
Transmitted Pulse: To
Received Pulses Pulse
Far Receiver
Near Receiver
DTLower2ft
OR..
TT3 - TT4
Extra time required to travel 2ft farther

31. Borehole Compensated Sonic
To remove certain borehole effects, we add another transmitter/Receiver set.
Now since these are identical (but upside down) we can take the average of the two
This is the BHC Delta-T or just DT
TT2
TT3
TT1
TT4

32. Sonde-Tilt TT’s, decreased and separated (UT TT’s will be larger)
First arrival amplitude will be dramatically smaller due to late arrivals on the long side of the borehole.
Zone of investigation is larger than 2’  DTTilted will be slightly larger than DTTrue.
E2 Will be slightly wider than normal.
Deviated Well

33. Eccentering TT’s, decreased.
First arrival amplitude will be dramatically smaller due to late arrivals on the long side of the borehole.
Low signal amplitude makes detection difficult since noise amplitude remains the same

34. Large Boreholes TT’s, Increased.
First arrival amplitude will be dramatically smaller due to increased travel time through the mud.
Low signal amplitude makes detection difficult since noise amplitude could remain the same
16 in is the maximum hole size.

35. Delta-T : BHC

36. BHC & HiRes BHC
2 ft
5 in
BHC
CBHC
HBHC

37. HiRes BHC SLS-EA (WA)’s were not designed to operate in this way.
The receivers are not exactly 5” apart.
A Master-Cal is required to correct for slight differences.
HRSPLTUT
5 in
HRSP
HBHC

38. Waveforms & Delta-T Far Receivers (TT1 & TT3)
Near Receivers (TT2 & TT4)
DT2ft
Extra time required to travel 2ft farther

39. Waveforms & Delta-T - Slow Formations
Far Receivers (TT1 & TT3)
Near Receivers (TT2 & TT4)
The slower the formation,
the larger separation
Faster Rock.
TTnear
From To to TTnear is also a factor of borehole size (TTMUD)
Slower Rock
DT Increases in slow formaitons

40. Waveforms & Delta-T - Borehole Size
Far Receivers
Near Receivers
The TT’s decrease due to
a decrease in TTmud.
DT is not affected.
DTsmall hole.
TTnear
From To to TTnear is proportional to borehole size (TTmud) and formation speed
DT Larger hole.

41. Detection
The transit time is “detected” where the waveform amplitude becomes larger than some threshold. This is called the “First Arrival”
Threshold E1 E2
Transit Time
For Open-Hoe Logging, we look for the second peak(E2), since it is usually larger than the first(E1)

42. DSLT Features Summary Max temp : 300 Deg F.
Not combinable with 60 Hz telemetry frame rate tools.
Digital waveform acquisition only.
DSLC is combinable with SLS-W (E), SLS-Z (F), SLS-C (D) modified sondes (FTB through wired).
CTS telemetry or DTS telemetry (both DTB and FTB interfaces are available in DSLC)..
Fixed digital sampling rate : 10 us.
A/D converter resolution for digital waveform : 16 bits.
Memory size for digital waveform : 510 words (1020 Bytes).
Variable telemetry frame size defined by the user :
- 26 words for the header.
- 0 to 510 words ( 1 word = 2 bytes) of data for 2 digital waveforms.
- Max of 536 words. (DTFS).
Telemetry frame rate = 15 Hz.
Firing rate = RATE (15Hz or 7.5Hz …).
2 waveform are acquired per sonic firing.
2 digital waveforms are sent uphole per frame.
TT detection done either downhole by the DSP or uphole by the HOST (DFAD).
2 acquisition modes (WMOD) : DETECTION (digitization interval centered on TT) or FULL (fixed digitization interval).
2 gains : hardware downhole gain and a software surface gain.
Amplitude normalization of the raw waveforms for VDL and waveform presentation.
2 type of waveform recorded : raw and normalized.

43. This is Noise Detection
Dt Detection Problems
Low amplitude of E2 may cause detection to occur on E4
This is Cycle Skipping
High noise may cause early detection
This is Noise Detection

44. CBL Good Bond Response
In excellent bond conditions, CBL amplitude may be too low that cycle skipping occurs to detect TT on E3.
In good bond conditions, TT may exhibit what is called TT shrinking